1. Field of the Invention
The present invention relates to the field of semiconductor processing and in particular, to the formation of an insulating layer for semiconductor devices.
2. Related Art
One prior processing technique for forming the nitride layer for a semiconductor device involves the use of plasma enhanced chemical vapor deposition. Here, a glow discharge is generated by the application of an rf field to a low pressure gas, thereby creating free electrons within the discharge region. The electrons gain sufficient energy from the electric field so that when they collide with gas molecules, gas-phase dislocation and ionization of the reactant gases (ammonia and silane or dischlorosilane) then occurs. The energetic species are then adsorbed on the surface.
However, semiconductor devices, such as field effect transistors, with nitride layers formed in this manner often exhibit bias-temperature instability. When the semiconductor devices are subjected to bias-temperature stress, the threshold voltage (V.sub.t) of the device shifts. In addition, the saturation current (Id.sub.sat) of the device also degrades under bias-temperature stress.
In addition, semiconductor devices with nitride layers formed in this manner could have relatively high diffusion contact resistance in the source and drain regions.
Moreover, semiconductor devices with nitride layers formed in this manner often experienced dopant segregation in the doped substrate regions. Dopant segregation occurs because subsequent exposure to high temperatures after doping causes the dopants to diffuse from the original doped substrate regions.
Thus, what is needed is a nitride layer and a process for forming a nitride layer for a semiconductor device that results in improved bias-temperature stability and improved diffusion contact resistance.
What is also needed is a nitride layer and process for forming a nitride which experiences reduced dopant segregation.